Low-level lead exposure in cultured astroglia: identification of cellular targets with vital fluorescent probes.

The effects of lead (0.0, 0.1, or 1 microM) on subcellular sites in primary astroglial cultures were quantitated with the use of vital fluorescent probes (fluorescence bioassays). Evaluation of cellular glutathione levels with monochlorobimane revealed a reduction in glutathione content after only 7 hr of Pb treatment to 77 and 82% of control values for 0.1 and 1.0 microM Pb, respectively. A further decrease in intracellular glutathione levels (to 74 and 56% of control values, respectively) was observed after 24 hr. Glutathione content returned to control levels by 48 hr, and exceeded control levels after 6 days (122 and 159% of control values) and 9 days (135 and 154% of control values) of lead treatment. Whereas glutathione has been shown by others to protect target organs from metal toxicity, these findings suggest a compensatory response by astroglia to the effects of Pb. Alterations in astroglial mitochondrial membrane potential were measured with the use of rhodamine 123. The membrane potential-dependent partitioning of rhodamine 123 was reduced following 14 days of Pb exposure (0.1 or 1.0 microM) to 75% of control value, indicating that Pb may act to dissipate the electrochemical gradient in astroglial mitochondria. Carboxyfluorescein diacetate was used to evaluate gap junctional intercellular communication (GJIC) between astroglia by fluorescence recovery after photobleaching. No difference between control and low-level Pb treated astroglia was found. Our results indicate that a Pb-stimulated increase in astroglial glutathione occurs after a lag period during which levels are decreased.(ABSTRACT TRUNCATED AT 250 WORDS)